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Full text of "Text Book Of Mechanical Engineering"

Appendix II.                            803

c, Fig. i2i#, which is first punched and roughed to shape, and
then placed in suitable dies; (3) the spanner A, Fig. 1210,
treated as in Fig. 767—that is, the jaw and shank are first scarfed
and welded as at A, then placed in dies ait B, arid finally punched
through at c before being removed; (4) the forked rod B, Fig.
121 a, similarly rough-forged, and punched in dies as at D, Fig. 767;
{5) the ring spanner E, Fig. 767, punched with a hexagonal punch;
{6) the hook F, Fig. 767, first roughly bent as at G, and then
stamped and punched as at H; and (7) the deep-eyed lever j,
Fig. 767, first prepared by two rough rings K K, and a scarfed
Tod L, then placed in the dies and drifted as shewn. Whenever
welding is done in the dies, the pieces must be raised to a very
good welding heat; see B and j, Fig. 767.

P. 125. Steelifying Iron.—This process is of the same
character as case-hardening, and is practised by making a powder
having i| oz. of prussiate of potash, \ oz. potassic nitrate, and
J oz. sugar of lead; placing it upon red-hot iron, and reheating
till the powder melts. Brightening a small portion of the iron,
the colour is watched for as in tempering, and the quenching
done in rain water. It is claimed that the hardening is very
thorough, and makes the material suitable for cutting tools.

P. 128. Hardening Steel.—The hardness produced in
•cooling steel depends very much on the rapidity with which the
heat is removed. Water is a good cooler, and is most used, but
much harder results are obtained by cooling in mercury, and the
hardest known by means of lead; the point of the tool, after
heating, being pushed into a block of cold lead.

Hydraulic Forging.—Advocates of hydraulic pressure for
heavy forging aver that steam hammers are done with, and that
no more heavy hammers will be ordered. Yet hydraulic forging
ivas used practically by Haswell in 1861, being proposed by
Charles Fox in 1847, and many big hammers have since been
built, proving that old prejudices die hard. At the same time
it is fully conceded that the hammer blow merely compresses the
•exterior of the forging, and never satisfactorily reaches the centre,
due evidently to the shortness of time occupied at each stroke.
The advantage possessed by hydraulic forging would belong also